This invention relates to a circuit arrangement for generating at least two interdependent supply voltages from an input voltage. Preferably, such interdependent supply voltages can be derived in a clocked power supply with a plurality of output voltages which are generated simultaneously by means of a converter. However, the invention also relates to any other type of power supply in which a plurality of interdependent supply voltages, for example, a plurality of supply voltages with a given ratio of the no-load voltages as for example across a plurality of secondary windings of a transformer, are derived from a common input voltage.
In such circuit arrangements one of the supply voltages can be controlled dependent upon the load to which it is connected, so as to influence the power supplied by means of the supply voltage in a load-dependent manner. As a result of this, the dependent other supply voltages will vary accordingly when the first-mentioned supply voltage is loaded. However, such a variation is undesirable.
In order to eliminate the influence of the load-dependent control of the first supply voltage on the dependent other supply voltage a separate control for each of the dependent other supply voltages may be provided, which serves to compensate for, on the one hand, the fluctuations caused by the load of the first supply voltage and, as the case may be, also of the dependent other supply voltages and, on the other hand, also the fluctuations of the dependent supply voltage caused by its own load. However, such a control, which is applied separately for each of the supply voltages, is very intricate for the mere reason that for each supply voltage a separate control loop is required and the power in the circuit powered by this supply voltage should be influenced by parts with a corresponding power rating. These parts alone already constitute a substantial part of the equipment. In addition, the control range of the individual control of each separate supply voltage is limited by the interdependence of the supply voltages. The control should compensate for the influence of the supply voltages on one another and for their own load dependence. This limits the accuracy and the control range of such control means in an undesirable manner. Moreover, the overall efficiency of a power supply of this construction deteriorates.
Another possibility could be to provide pre-loads for the individual interdependent supply voltages, enabling the dependent supply voltages to be adapted to the load of the regulated supply voltage. Apart from the substantial number of circuit elements required for this, it gives rise to very high losses, particularly in certain operating points, thereby drastically reducing the overall efficiency of the power supply.